1. Field of the Invention
The present invention generally relates to the field of data communications, specifically, data communications between circuit boards within the same housing.
2. Related Art
Data communications has become a pervasive part of every day life and it""s expected that personal computers (PCS) and modems will one day be as ubiquitous as televisions are today. Millions of people world wide use their PCS and modems to share and access information on the Internet or public on-line service. To connect to the Internet or other network, a person utilizes the services of a Network Service Provider (NSP). An NSP deploys and maintains the hardware that enables a person with a computer and modem to connect to the Internet or other network. The hardware provided by an NSP for enabling a person to connect to the Internet is called a terminal server. A person uses their modem and the public switched telephone network (PSTN) to connect to an NSP""s terminal server. The terminal server provides the necessary connectivity to the Internet.
FIG. 1 is a network diagram illustrating a variety of users accessing the Internet through a typical NSP. As illustrated in FIG. 1, office user 101 utilizes a router 106 with an ISDN connection to gain network access, mobile user gains network access with a V.34 modem, and home user obtains network access using a 56 kilobits per second modem. Each of the users connect to the NSP point of presence (POP) 120 through the PSTN 140. NSP POP 120 includes a terminal server 122, a local area network (LAN) 126, a server 128 connected to the LAN 126, and a router 124. The terminal server 122 is connected to the PSTN 140 through T1 circuit 150. PSTN 140 time division multiplexes the data it receives from each user 101, 102, 104 onto T1 circuit 150. A T1 circuit in channelized form is a telephone circuit that can carry up to twenty four channels of time division multiplexed (TDM) data of any type (e.g., voice, text, and video). Consequently, a terminal server with a single T1 connection can receive channelized TDM data from twenty four separate users. NSPs utilize T1 circuits to reduce the number of phone lines that they have to purchase from the phone company. This provides a cost and management advantage.
Typically, terminal server 122 includes twenty four modems to process the twenty four possible simultaneous modem sessions that it could receive via a channelized T1 circuit 150. The terminal server processes the modem sessions to recover the data transmitted by the users. The user data is then encapsulated in a protocol and transmitted onto LAN 128. Router 124 receives the encapsulated user data and routes it through the Internet to the intended destination.
As Internet usage continues to grow dramatically, NSPs constantly need to keep pace with the increased demand. One way for the NSPs to accomplish this is simply to purchase additional T1 circuits from the phone company and purchase additional terminal servers to handle the increase in users. A problem with this approach is that the NSPs will have to manage multiple T1 circuits and multiple terminal servers.
What is needed is a single hardware unit that can process a great deal of simultaneous user sessions, provide scalability, and provide an easy migration path to new technologies.
The present invention provides a system for transmitting channelized time division multiplexed data between circuit boards within a housing. The present invention can be used to create a scalable remote access server for providing network access to a large number of users. The scalable remote access server also provides an easy migration path to new technologies.
A unique feature of the present invention is that the housing does not include a TDM bus for transmitting TDM data between the circuit boards placed in the housing. Rather, in one embodiment of the present invention, the housing includes a switch card for transmitting TDM data between any two circuit boards in the housing. The switch card includes a switching matrix having at least a first data port and a second data port. A first data bus connects a first circuit board within the housing to the first data port of the switching matrix, and a second data bus connects a second circuit board within the housing to the second data port of the switching matrix. The first circuit board transmits TDM data to the second circuit board by transmitting the TDM data together with a destination port identifier to the switching matrix. The destination port identifier identifies the data port of the switching matrix to which the second circuit board is connected. The switching matrix receives the TDM data and the destination port identifier from the first circuit board and then transmits the TDM data onto the bus connected to the port identified by the destination port identifier, thereby transmitting the TDM data from the first circuit board to the second circuit board.
A scalable remote access server that can process a large number of simultaneous user sessions and provide an easy migration path to new technologies is created by placing a first networking card in one of the slots of the housing and placing one or more second networking cards in one or more of the remaining slots.
A first networking card according to one embodiment of the present invention includes a first port adapted to connect to a communications circuit used to transmit a first signal. The first networking card also includes a demultiplexer that receives the first signal and extracts a set of second signals from the first signal. A packetizer within the first networking card receives the set of second signals. The packetizer includes a plurality of buffers for buffering data from each of the plurality of second signals. The data accumulated in each buffer is transmitted to the switching matrix together with a destination port identifier. The switching matrix forwards the data to one of the second networking cards based on the destination port identifier. The second networking cards further process the data.
A second networking card according to one embodiment includes a first port adapted to connect to the switching matrix, a T1 generator for creating a set of digital signals using the data received from the switching matrix, a multiplexer for multiplexing the set of digital signals onto a bus, and a plurality of modems and a high level data link control (HDLC) controller connected to the bus for processing the digital signals. The second networking card can also include a point-to-point protocol (PPP) processor and a router.
In one embodiment, the communications circuit that the first networking card is connected to is an optical facility, such as an optical fiber, and the first signal is an OC-3 formatted signal. In another embodiment the communications circuit is a T3 circuit, and the first signal is a formatted synchronous digital signal, such as a DS3 digital signal. A DS3 signal includes twenty-eight DS1 signals and each DS1 signal includes twenty-four DS0 signals. That is, twenty-four (24) DS0 signals are time division multiplexed to from the DS1 signal and twenty-eight (28) DS1 signals are time division multiplexed to from the DS3signal. A DS0 signal has a transmission rate of 64 kilobits per second (kbps). Each DS0 signal can be associated with a modem or ISDN session. Therefore, the first networking card can receive time division multiplexed (TDM) data from up to six-hundred-seventy-two modems or ISDN terminals. This data is transmitted through the switching matrix to one or more of the second networking cards. The second networking cards have processors for processing the TDM data and performing routing, among other functions. In this manner, the remote access server according to the present invention can provide a large number of users with network access.
Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.